Make trainee maintainers three times as likely to be picked
Make trainee maintainers three times as likely to be picked

Trainee maintainers count as reviewers, but should get more reviews than
most reviewers, as they need practice to become a maintainer. This makes
them three times as likely to be picked (compared to another reviewer;
compared to before, it's roughly twice as likely at the current numbers
for each).

Also, switch to `Array#sample` because I think it looks nicer.

stoplightio/gitlabhq,mmkassem/gitlabhq,iiet/iiet-git,mmkassem/gitlabhq,iiet/iiet-git,mmkassem/gitlabhq,stoplightio/gitlabhq,mmkassem/gitlabhq,iiet/iiet-git,stoplightio/gitlabhq,stoplightio/gitlabhq,iiet/iiet-git